1. Field of the Invention
This invention generally relates to a retro-reflective scanner operative for electro-optically reading indicia having parts of different light reflectivity, for example, bar code symbols, and, more particularly, to eliminating collection optical components in the return path along which light reflected off the indicia travels.
2. Description of Related Art
Various optical readers and optical scanners have been developed heretofore to optically read bar code symbols applied to objects in order to identify the object by optically reading the symbol thereon. The bar code symbol itself is a coded pattern comprised of a series of bars of various widths and spaced apart from one another to bound spaces of various widths, the bars and spaces having different light reflecting properties. The readers and scanners electro-optically decoded the coded patterns to multiple digit representations descriptive of the objects. Scanners of this general type have been disclosed, for example, in U.S. Pat. Nos. 4,251,798; 4,360,798; 4,369,361; 4,387,297; 4,593,186; 4,496,831; 4,409,470; 4,460,120; 4,607,156; 4,673,805; 4,736,095; 4,758,717; 4,760,248; 4,806,742; 4,808,804; 4,825,057; 4,816,661; 4,816,660; 4,835,374; 4,845,350; 4,871,904; 4,896,026 and 4,923,281, all of said patents having been assigned to the same assignee as the instant invention and being hereby incorporated herein by reference.
As disclosed in the above-identified patents, a particularly advantageous embodiment of such a scanner resided, inter alia, in emitting a light beam, preferably a laser beam, emitted from a light source, preferably a gas laser or a laser diode, and in directing the laser beam along an outgoing path to a symbol to be read. En route to the symbol, the laser beam was directed to, and reflected off, a light reflector of a scanning component. The scanning component moved the reflector in a cyclical fashion and caused the laser beam to repetitively scan the symbol. The symbol reflected the laser beam incident thereon.
In a retro-reflective scanner, a portion of the incident light reflected off the symbol was collected in a return path by collection optics, and detected by a detector component, e.g. a photodetector, of the scanner having a field of view. The purpose of the collection optics is to increase the amount of light reaching the detector, and to limit the field of view of the detector to minimize the amount of ambient light that reaches the detector. The detected light over the field of view was converted into an electrical signal which, in turn, was decoded by electrical decode circuitry into data descriptive of the symbol for subsequent processing. The cyclically movable reflector swept the laser beam across the symbol and swept the field of view during scanning.
There were several different types of collection optics disclosed in the known retro-reflective scanners. For example, U.S. Pat. No. 4,409,470 disclosed a convex lens in the return path. U.S. Pat. No. 4,816,660 disclosed a concave collecting mirror in the return path. Such optical components occupied space, were required to be accurately positioned, and represented an expense, not only in manufacturing, but in assembly costs--all factors which are desired to be avoided.